Process and apparatus for treating suspensions



June 9, 1959 F. J. FONTEIN 2,889,925

PROCESS AND APPARATUS FOR TREATING SUSPENSIONS Filed Oct. 12, 1956 2 Sheets-5heet 1 4 t FIG.I

June 9, 1959 F. J. FONTEIN 2,889,925

PROCESS AND APPARATUS FOR TREATING 'SUSPENSIONS Filed Oct. 12, 1956 2 Shee ts-Sheet 2 FIG. 2

' rnR/vsrs United States Patent PROCESS AND APPARATUS FOR TREATING SUSPENSIONS Freerk J. Fontein, Heerlen, Netherlands, assignor to Stamicarbon N.V., Heerlen, Netherlands Application October 12, 1956, Serial No. 615,602 Claims priority, application Netherlands October 14, 1955 7 Claims. (Cl. 209-1725) The present invention relates to a process for treating undiluted and diluted suspensions in a closed circuit, in which the diluted suspension is thickened in a static or gravity thickener and is continuously recycled, together with the undiluted suspension, into the circuit for use.

Such a process is used, among others, in coal and ore washeries operating with suspensions, where the material to be treated is separated by means of this suspension into a fraction of low specific gravity and a fraction of high specific gravity.

After leaving the washing plant the two material fractions contain greater or smaller quantities of the separating suspension, which, in many cases, must be recovered so far as possible, due to the high cost of the weighting material (the suspension solid). Usually this recovery is effected by letting both fractions drain on screens and subsequently rinsing them, thickening the so diluted suspension in a thickener, and then returning the thickened suspension to the starting point of the washing treatment. In such washing plants it is customary to mount, beside each other, a collecting tank with a. pump for the undiluted suspension, and a thickener for the diluted suspension with a pump for the thickened arranged behind it. A principal object of the present invention is to provide a simplification of this well known process.

In accordance with the invention the undiluted suspension is fed into the thickener for the diluted suspension, to a position substantially over the discharge aperture of the thickener, at a level below the liquid level in the thickener and below the level at which the diluted suspension is supplied, and is then fed, together with the thickened suspension, to the place where the suspension is used. By this expedient the collecting tank and the lift pump for the undiluted suspension may be eliminated.

It is important that at the level where the undiluted suspension is added to the thickening diluted suspension, the concentration of the thickening suspension should be as high as that of the undiluted suspension, to avoid dilution of the latter. Therefore, in accordance with the invention the undiluted suspension is added to the suspension being thickened at a level in the thickener whereat the suspension being thickened has attained substantially the same concentration as that of the undiluted suspension. It is preferred to add the undiluted suspension as close as possible to the discharge aperture of the thickener. As a result, the undiluted suspension will not materially affect the thickening process, so that the dimensions of the thickener may be determined exclusively by the demands made thereon by the amount and initial concentration of the diluted suspension which is to be thickened.

The invention also relates to apparatus for carrying out the process, including a static thickener for the diluted suspension provided with feeding means for the undiluted suspension, which feeding means discharges substantially over the discharge aperture of the thickener,

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at a level below the overflow level of the thickener and below the outlet of the feed means for the diluted suspension. Preferably, the feeding means for the undiluted suspension discharges into the thickener at a level not more than one third of the height of the thickener above the discharge aperture. The invention further relates to washery circuits in which the process and apparatus are employed.

Since the concentration of the diluted suspension supplied to the thickener may be subject to fluctuations, the feed outlet through which the undiluted suspension discharges into the thickener may be vertically adjustable. By this expedient it is possible to feed the undiluted suspension into the thickener at a level whereat the suspension being thickened has already attained a concentration corresponding substantially to that of the undiluted suspension, at all times.

By Way of non-limiting example, the invention will'be explained with reference to the drawings, in which Figure 1 is a fiowsheet of a coal or ore washery in which magnetite is used as the weighting material, and Figure 2 is an enlarged detail view illustrating means for vertical adjustment of the feed tube for the undiluted suspension.

In Figure 1, a mixing funnel 1 is fed by a filling trough 2, into which the material to be washed, for example deslimed coal or ore with dimensions ranging between /2 and 8 mm., is fed at 3, and the separating suspension needed for the washing treatment is fed at 4. The mixing funnel 1 is connected through a conduit 5 to a washer such as the hydrocyclone washer 6.

The overflow from the hydrocyclone, which contains the bulk of the material particles of low specific gravity together with separating suspension, is discharged through conduit 7, and the apex discharge fraction from the hydrocyclone, which contains the bulk of the material particles of high specific gravity together with separating suspension, discharges through conduit 8.

From conduit 7, the overflow fraction is passed across a sieve bend 9 with slots of 1 mm., where the greater part of the suspension passes through the slots and is collected in the collecting funnel 14. As will be apparent, the suspension collected in funnel 14 is undiluted. The overflow from sieve bend 9 is passed across a vibrating screen 10, 11 with apertures of 0.4 mm, where on the first part 10 undiluted suspension drips off into funnel 16. On the second part 11 of the screen the material is rinsed with rinsing Water supplied through conduits 17 to sprays 12, and is then discharged at 13. The suspension diluted with water passes through screen part 11 into funnel 18, and is discharged through conduit 20 by means of a pump 22. The undiluted suspension caught in funnel 16 passes through conduit 19 to join the undiluted suspension collected in funnel 14, which passes through conduit 15. All the undiluted suspension passes on through conduit 21 to the thickener 30.

Separating suspension is recovered from the high specific gravity fraction in the same way. This fraction is discharged from conduit 8 and passed over sieve bend 9' and then over vibrating screens 10, 11'. On screen part 11 the material is rinsed with water supplied through conduit 17 to sprays 12. Undiluted suspension is collected in funnels 14 and 16', and passes through conduits 15 and 19' to conduit 21. The diluted suspension is collected in funnel 18, and fed through conduit 20 to pump 22. The heavy material (shales) are discharged at 13. As will be seen, all of the undiluted suspension, consisting of the underflow from sieve bends 9 and 9' and from screens 10 and 10', is collected together and sent to the thickener 30 through conduit 21.

which, containing the fine magnetite particles, is sent. to

the thickener 3t) through conduit 25. The apex discharge fraction from the hydrocyclone classifier 24,

which contains the coarser magnetite particles and impurities, is sent through conduit to to the magnetic separator 27. From the magnetic separator impurities and water are removed through conduit 28, and the magnetite caught in. the magnetic separator is led through CG; it 29 into conduit 25.

The thickener 30 is provided with an annular well 3 preferably mounted concentrically therein. The well 31 projects upwardly above the overflow level of the thickener and extends downwardly into the liquid. Concentrically mounted inside the well 31 is a tube 32 of smaller diameter, which also projects upwardly above the overflow level of the thickener and extends downwardly into the liquid, extending downwardly, however, to a deeper level than does the well 31, and preferably into the conical part of the thickener. The dilute suspension to be thickened is introduced into the thickener in the space between well 31 and tube 32, while the undiluted suspension is fed through conduit 21 into the tube 32. The tube 32 by conventional means may be capable of displacement in the axial or vertical direction, or its lower end may be provided with an extension 37 adapted to be displaced or relatively adjusted in axial direction, so that the level where the undiluted suspension is dischanged into the thickener may be varied in either vertical direction, as circumstances may require. The extension 37, for example, may be adjustably engaged to the tube 32 by screw threads. As shown in Figure 2, the tube 32 is provided with external screw threads 38, to which the extension 37 is threadably engaged. The extension 37 may be conveniently provided with conventional means, such as lugs 39, to facilitate rotational adjustment thereof.

In this way, the diluted suspension may settle in the thickener without interference by the ruidiluted suspension, and discharge of water free of weighting material and containing impurities via overflow 33 is possible. The overflow water is conducted by means of the conduit 34 to the sprayers 12 and 12. If desired, the tube 32 may be an elongation or extension of conduit 21.

Since the tube 32 extends downwardly into the lowermost part of the thickener, where the diluted suspension has already been thickened sufliciently, there is no danger that the undiluted suspension will be diluted by the diluted suspension. The undiluted and the thickened diluted suspension are drawn oil together and pumped by the single pump 35 through conduit 36 to trough 2, and thereby recycled for further use.

It will be evident that the illustrative flow diagram may be altered in many respects without departing from the scope of the invention. Instead of the hydrocyclone 6, for example, any other washer operating with a heavy medium may be used. Similarly, the illustrated arran'gement of sieve bends and screens may be replaced by similar elements. The sieve bends 9 and 9' are preferably of the type described in United States patent application Serial No. 475,251, filed December 14, 1954.

I claim: 1. A process of treating separately collected undiluted and diluted suspensions in a circuit comprising the steps of thickening the diluted suspension in a static thickener,

feeding the undiluted suspension into the thickener at a position substantially above the discharge aperture thereof and at a level whereat the diluted suspension being thickened has attained substantially the same concentration as that of the undiluted suspension, and withdrawing the undiluted suspension fromthe thickener underflow together with the thickened fraction of the diluted suspension.

2. A continuous washing process comprising the steps of separating material into high and low specific gravity fractions by means of a separating suspension, recovering some of the separating suspension from the material fractions in undiluted state, rinsing the material fractions to recover more of the separating suspension therefrom in diluted state, thickening the diluted suspension in a static thickener, feeding the undiluted suspension into the thickener at a position substantially above the discharge aperture thereof and at a level whereat the diluted suspension being thickened has attained substantially the same concentration as that of the undiluted suspension, withdrawing the undiluted suspension from the thickener underfiow together with the thickened fraction of the diluted suspension, and returning the suspension mixture withdrawn from the thickener underflow to the separation step.

3. A process as defined in claim 2, wherein the uniluted suspension is fed into the thickener at a level not more than one third of the height of the thickener above the discharge aperture thereof.

4-. A process as defined in claim 2, including the step of adjusting the level at which the undiluted suspension is introduced to correspond to the level whereat the diluted suspension being thickened has attained substantially the same concentration as that of the undiluted suspension.

5. In a static thickener having a central discharge aperture in the lowermost portion of the bottom thereof, an annular well mounted centrally in said thickener, siad well projecting upwardly above the overflow level extending downwardly to a substantially deeper level than does said well to a position substantially above the discharge aperture of said thickener, means for feeding a diluted suspension to the space between said Well and said tube, and means for feeding undiluted suspension.

into said tube, said tube extending downwardly to a level whereat the diluted suspension being thickened in the thickener has attained substantially the same concentration as that of the undiluted suspension.

6. Apparatus as defined in claim 5, wherein the lower end or" said tube is adjustable in vertical direction.

7. A wasliery comprising means for mixing particulate r aterial with a separating suspension, a washer for seo ing said mixture into high and low specific gravity fractions, means for recovering suspension from said separated fractions in undiluted state, a static thickener having a central discharge aperture in the lowermost portion of the bottom thereof, an annular well mounted centrally in said thickener, said well projecting upwardly above the overflow level of the thickener and extending downwardly below said level, a tube of diameter smaller than said well mounted concentrically inside said well, said tube projecting upwardly above the overflow level of the thickener and extending downwardly to a substanially deeper level than does said well to a position substantially above the discharge aperture of said thickener, means for conducting the suspension recovered in diluted state to the space between said well and said tube, means for conducting the suspension recovered in undiluted state into said tube, said tube extending downwardly to a level.

References Cited in the file of this patent UNITED STATES PATENTS 2,690,261 Maust Sept. 28, 1954 a Chance Feb. 27 1934-" 

